Historically, decorated metal control panel information plates have been used in conjunction with mechanical switches, timers and actuators to allow the consumer to control a machine such as a washer, dryer, range or stove. These mechanical devices have stems that protrude through holes of vaious sizes in the graphics portion of the control panel which is decorated by a stylized presentation of information describing available functions to the consumer. The stems are capped by knobs and buttons that tend to cover or extend beyond the holes and finish the control panel. All this complexity makes it difficult for the consumer to clean the control panel while mechanical switches are expensive and losing desirability because of cost and a growing perception that they are "old" or "outdated" technology.
More recently, touch sensitive switches have been used extensively to replace mechanical switching devices. Examples of such touch sensitive switches may be found in U.S. Pat. Nos. 4,975,676; 4,065,649; 4,228,330; 4,394,547; 4,639,559; 4,818,827; 4,901,074 and 5,747,757. One type of touch sensitive switch that is commonly employed in connection with control panels is membrane switches. U.S. Pat. No. 5,747,757 specifically concerns a control panel comprising a membrane switch. Membrane switches generally comprise a combination of a decorated information plate and functional circuitry. The movement towards membrane switches was driven by lower cost and a consumer base who appreciates ease of cleaning. These membrane switches are typically flat, thin and flexible. They are added to the top surface of the control panel support by an adhesive. Inherently, they have a ribbon connector which is fed through a hole in the support for connection to other control circuitry.
Membrane switches in many applications such as shown in U.S. Pat. No. 5,747,757 are laminated or adhered to the surface of a steel or aluminum supporting plate to form the control panel. During manufacturing there is a problem of aligning the sticky back of the membrane circuit to the supporting face intended to hold it. Placement of the membrane switch in many applications is critical to the aesthetic and function, especially where a see-through window is required for a clock, lights or other device requiring alignment. Once the membrane has been placed, the adhesive makes it impossible to remove and reposition so the combination of membrane and support base has to be discarded or used with the defect if alignment is not proper.
Membrane switches in many applications require the use of a polycarbonate decorated face. The polycarbonate face provides better wear resistance because the polyester of the membrane is easily scratched and polycarbonate is a better window material because of its superior transparency and resistance to scratching. However, this specialization increases the cost of the membrane switch circuit and graphics combination.
Once the decorated membrane switch circuits are laminated to a supporting surface, the edges sometimes do not stick or they turn up over time creating a poor aesthetic look. Even a properly placed laminate that is brand new can appear wavy and uneven looking. Poor attachment at the edges causes the consumer to feel that the device is falling apart or old. This edge is also exposed to cleaning operations and chemicals during cleaning which exacerbates the problem. The control panel of the present invention is not susceptible to such a problem.
The control panel of the present invention allows one to create switching circuitry using the support substrates by themselves, without the addition of a separate switching device such as a separate membrane switch assembly. The supports and the switch circuitry are integral. One supporting surface is thus also the decorated panel itself. This approach eliminates the need for a stick-on membrane switch or assembly and thus it provides a less expensive and more robust control panel. It further improves the ease of cleaning experienced by the consumer because there are no edges that can furl and no plastic to scratch. The control panel of the present invention is flat and continuous and it is also design versatile. Where desired, it can accommodate and support knobs or buttons, or large devices such as mechanical timers. Materials used to decorate the surface are robust and lend themselves to screen printing and sublimation transfer imaging. Moreover, the control panel employs an inner support panel upon which circuitry is formed that is highly durable. This inner support panel comprises super-durable porcelain enameled metal.